The most effective means for isolating biomacromolecule are chromatography and capillary electrophoresis at the present time. In conventional process for purifying biomacromolecule, reagents such as SDS (sodium dodecyl sulfate), TX-100, CTAB (cetyl trimethylammonium bromide, CTAB), guanidine hydrochloride, GuSCN (guanidinium isothiocyanate) and the like are used to lyse the cells, so that polysaccharide, plasmid DNA, and RNA are extracted into the upper phase and protein is denatured and precipitated in the phase middle or is distributed into the phase middle partly. But still a small amount of high hydrophilic protein is distributed into the upper phase, and components cannot be isolated effectively and quickly from each other. Genomic DNA and lipid are released into the supernatant, and then protein is extracted and removed by phenol and chloroform (toxic), finally plasmid DNA is precipitated in the presence of ethanol or isopropyl alcohol and is recovered. However, a large amount of protein, lipopolysaccharide and polysaccharide are remained in such purified plasmid DNA, and they make a bad influence on many important biological experimental results. More particularly, biological researches such as cell transfection, gene treatment, DNA bacterin immunity and the like have higher requirement on the purity of plasmid DNA, and such a process hardly obtains a desired purity and other purifying processes are to be used to isolate and purify plasmid DNA.
Purifying plasmid DNA with DEAE-silica resin has been disclosed in another document. There is phosphate radical in DNA molecule and thus makes it negative. The density of DEAE group on silica is substantially higher than that on conventional polysaccharides resin, which makes DNA combined to the resin with high DEAE density more firmly and very high salt concentration is necessary to elute DNA. But other impurities such as protein can be eluted in lower salt concentration so as to be isolated from DNA entirely. Such a case will occur only when anions such as SDS (sodium dodecyl sulfate) are not combined to the surface of biomacromolecule. However, in fact, a large amount of denatured protein, LPS, and polysaccharide combined with SDS is remained in the supernatant containing plasmid DNA. SDS molecule has sulfate radical on it and shows negative, and can combine with molecules such as protein firmly resulting in carrying plentiful negative charges on the surface of these molecules, which changes the original chromatography activity to a great extent and makes an essential change on the elution conditions of protein, LPS and polysaccharide, and it is difficult to isolate DNA from impurities such as protein, LPS thoroughly.
Chinese patent application CN 1378592A has disclosed a process for purifying plasmid DNA using tangential flow filtration without RNA enzyme and organic solvent, the process comprising: (a) digesting the cells; (b) culturing the cells for 4˜24 hours for lysing and dissolving, but not enzymatic digesting RNA; (c) removing lysing impurity from the cells for providing a solution of plasmid DNA; (d) filtrating the solution by tangential flow filtration means so as to obtain reflux solution containing plasmid DNA; (e) recovering the reflux solution. The undesired result has been gained in the isolating speed and effect by using the above process.